Powder injection molding includes three steps: a sintering compound molding step in which power of a metal for example is mixed with other components such as a resin binder, under heat until the mix is fluid, and then the mix is injected to form a molded body; a debinding step in which the molded body is heated to remove the resin binder; and a sintering step in which the molded body is heated at a higher temperature until the powder is sintered. When the powder is provided by a metal, the method is commonly known as MIM (Metal Powder Injection Molding) method, and is widely used in manufacture of metal objects such as metal parts having complex geometries.
Powder injection molding uses essentially the same injection molders as used in plastic injection molding. However, since the feedstock contains a greater ratio of sintering powder than the resin binder, there is a problem that the intermediate, i.e. the body as injection molded, is lower in strength than typical resin products manufactured by injection molding. In particular, due to the debinding and sintering steps that must follow the step of injection molding, handling is often difficult between these steps. Typically, molded bodies of a complicated shape are often damaged while they are being moved for the next step.
In addition, due to the lower strength of the molded body, the body is often damaged when removed from the mold. This poses a special difficulty in the removal of a small body or a body which has a complicated shape.
In typical resin injection molding, small bodies are connected via a runner in a single mold, then formed in a single shot, and a resulted tree of the bodies are often handled as a single piece. However, this is very difficult in powder injection molding. Because of lower strength of the molded body, a plurality of bodies connected via a runner and molded in a single injection is very difficult to release from the mold. Therefore, producing a small body of a complicated shape by means of powder injection molding greatly decreases production efficiency.
In recent years, there have been attempts to employ LIGA (Lithographie Galvanoformung Abformung) processes in the production of metal mold sets for resin injection molding, as part of various efforts to build so called micro machines. However, for the reasons described above, it has been very difficult to make micro machines from powder injection molded bodies containing a metal or a ceramic.